This invention relates to an inductance element, for example, for use in power supply units of computers.
FIG. 8 shows an example of a circuit of a step-down type DC/DC converter for use in the power supply unit of computers. Reference numeral 101 denotes a control IC, reference symbol VB denotes a source of voltage supply, reference numeral 102 denotes a switching circuit, reference numeral 103 denotes a load for CPU or others, and reference numeral 106 denotes a capacitor.
The switching circuit 102 consists of switching devices 105a, 105b connected to output terminals S, T for driving of the control IC 101, and an inductance device 104 connected between an output terminal U of the switching devices 105a, 105b and the load 103.
In the above construction, load current from several amperes to dozens of amperes flows through the load 103 connected between an output side of the inductance device 104 and earth, and at the same time high current flows through the inductance device 104. The inductance value of the inductance device 104 is varied in response to variation in load and switching operation of the switching circuit 102. Therefore, when the inductance value of the inductance device 104 is varied, the operation of the switching circuit 102 becomes unstable. By the way, in a conventional manner, because operating (switching) frequency of the control IC 101 and the switching devices 105a, 105b used for the above circuit is not so high, as the inductance device 104 used for the switching circuit 102, one whose inductance value is about dozens of xcexcH (micro henries) has been used. Moreover, as the construction of the inductance device 104 above, for example, wide-core wire is merely wound around a wide-core drum-shaped ferrite core at a predetermined number of times.
In recent years, along with the advance of technology, the operating frequency of the control IC 101 and the switching devices 105a, 105b above becomes quite high, as the inductance device used for the DC/DC converter circuit above, one whose inductance value is not more than 1 xcexcH has been required.
Furthermore, together with the control IC 101 and the switching devices 105a, 105b, the performance of CPU has been improved to speed up. If said CPU is applied as the load of the DC/DC converter circuit, the CPU will be very heavy load therefor (the load current will be very high). However, the inductance device of construction in which wire is wound around the conventional drum-shaped ferrite core is difficult to make the inductance value thereof minute value of not more than 1 xcexcH, cannot provide stable inductance value when high current about dozens of amperes flows, and also is in the difficult state to be minimized in the dimensions.
The present invention is made to meet the requests for the inductance device above, and an object thereof is to provide an inductance device whose dimensions can be minimized, which has an inductance value of not more than 1 xcexcH, and whose DC characteristic is almost flat even if high current flows.
In order to achieve the above object, an inductance device according to the present invention for use in power supply units is characterized in that a slit is provided on one surface of a polygonal cylindrical ferrite core in the same direction to the depth direction of a tube hole, and a conductor is inserted through the tube hole. Besides, the inductance device is further characterized in that the conductor is wound to pass through into said tube hole two or more times. Moreover, the inductance device is characterized in that the conductor is a plate one.
Besides, the inductance device according to the present invention for use in power supply units is characterized in that the ferrite core is shaped into square cylindric, a slit is provided in one side of the ferrite core in the same direction to a hollow portion to form an open magnetic path, and a belt-like conductor is inserted through the hollow portion. Moreover, the inductance device is characterized in that each end of the belt-like conductor inserted through the hollow portion of the square cylindrical ferrite core is formed into a surface mount terminal.